Physiological responses of Sargassum fusiforme seedlings to high-temperature stress

Temperature fluctuations due to the global warming and frequent abnormal heat waves cause physiological and metabolic disorders in Sargassum fusiforme seedlings, especially at the early stage of marine culture. In this study, 3 temperature levels (20, 25, and 30 °C) were used to analyze the effects of short-term high temperatures on the growth and metabolism of S. fusiforme seedlings. The results showed that, although S. fusiforme seedlings were tolerant to high-temperature shock, high temperature (30 °C) significantly reduced the electron transfer rate, nitrogen assimilation-related enzyme activities and soluble protein content in S. fusiforme seedlings. Moreover, the short-term high temperature induced more malondialdehyde content and enhanced superoxide dismutase activity and dark respiration rates. However, under high-temperature conditions (30 °C), peroxidase activity did not increase significantly when compared with the activity at 20 °C. This phenomenon was not conducive to the scavenging of intracellular reactive oxygen species, resulting in the gradual decay and death of young seedlings. The results of this study suggest that photosynthesis in seedlings is sensitive to a short-term increase in seawater temperature. Because of extreme temperature disturbances, including heat waves, the cultivation management of the economic seaweed presents challenges.